R-245fa is a useful compound which can be used for an alternative for CFC (chlorofluorocarbon) or HCFC (hydrochlorofluorocarbon) used as a cooling medium and a foaming agent and which is not likely to destroy the ozone layer.
R-245fa can be produced by fluorination of 1, 1, 1, 3, 3-pentachloropropane using HF. In this production process, since an excessive amount of HF is used for the reaction, a reaction mixture contains a considerable amount of unreacted HF in addition to produced R-245fa, and also may contain, in addition to these, a by-product (for example, R-244fa (1, 1, 1, 3-tetrafluoro-3-chloropropane) and so on). A composition of such a reaction mixture is determined by reaction conditions, and in order to obtain R-245fa from the reaction mixture as described above, the mixture is subjected to separation/purification. Further, it is desirable to recover the unreacted HF from the reaction mixture and re-used for the reaction.
In the present specification, the term “separate/purify” is intended to mean such that when a mixture stream comprising specific two components (for example, R-245fa and HF) is subjected to a certain processing step (for example, a distillation step) and thereby other stream is obtained in which stream a ratio of a concentration (a) of one specific component (for example, R-245fa) to a concentration (b) of the other specific component (for example, HF) of the stream (namely a ratio [a/b]) is increased, that is when the ratio [a/b] is increased to [a′/b′] (wherein a′/b′>a/b), the specific component (R-245fa) is said to be separated/purified.
Further, in the present specification, the term “separate/purify” is intended to not necessarily mean perfect separation, and such term is used to include a fairly broad meaning so that it includes a concept of so-called “concentration.” However, in one of the most preferable embodiments, the term “separate/purify” is intended to mean that a mixture stream consisting substantially of two specific components is subjected to a predetermined step so that other stream is obtained which contains substantially only one specific component. In another embodiment of the most preferable embodiments, the term “separate/purify” is intended to mean that a mixture stream consisting substantially of two specific components and at least one component is subjected to a predetermined step so that other stream is obtained which is substantially free from one of the specific components.
When R-245fa is separated/purified from a reaction mixture as described above, alkaline washing and/or water washing is usually used for the separation of unreacted HF from R-245fa (and other HFC if any). However, separated HF in such a manner is present in an aqueous solution and there is no other way than disposing it. Thus, the above mentioned separation not only wastes HF but also requires additional cost for washing and disposing. Therefore, it is desirable to provide a process of more effectively separating/purifying R-245fa and/or HF from a mixture of HF and R-245fa.
As to other HFCs such as R-134a (1, 1, 1, 2-tetrafluoroethane), there are examples in which using an azeotropic mixture of HF and the HFC, separating R-134a is separated from a mixture containing those compounds (see, for example, Japanese Patent Kokai Publication Nos. 4-261126 and 5-178768). However, with respect to the separation of R-245fa and/or HF from a mixture of R-245fa and HF, the presence of an azeotropic mixture of R-245fa and HF has not been known.